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Subsystem Overview

The primary objective of the Electrical and Power Systems (EPS) is to distribute adequate power to all of the subsystems. To accomplish this, M-Cubed utilizes both a battery and solar arrays placed on every side of the cubesat. The power collected by the solar cells is sent through current and voltage sensors connected to the microcontroller and then through a 5V voltage converter, where is it dispersed between active buses controlled by switches (during Discharge Mode) or to the battery charger (during Charge Mode). When M-Cubed is in Discharge Mode, the solar cell power is supplemented by the battery power through either a 3.3 V or 12 V voltage converter to power other buses. In Charge Mode, the microcontroller opens all switches to remove power from all other subsystems and directs all solar power through the battery charger. The entire satellite is expected to require 1.2 Watts (W) of average power and 4.7 W of peak power.

While M-Cubed is in eclipse, all components will be in low-power or standby mode. If the cubesat is in sunlight and takes a picture, the shutter, camera, and microcontroller will all need full power to operate. After a useable picture is taken, the cubesat will wait again in low-power mode until it enters the ground station coverage area at which point the transmitter will be switched to full power mode. A versatile power system requiring the use of a rechargeable battery system is necessary to accomplish these tasks.

Solar Arrays

Solar arrays cover each side of M-Cubed and send power through the main circuit board to be sent to various components on the satellite in 3.3 V, 5 V and 12 V power-buses. On the way to the main circuit board, the power is passed through a charging circuit, where the power is either stored in the battery during the charging phase or, if necessary, supplemented with power from the battery. These arrays are also used by the orbits and controls subsystem to create a sun direction vector used to calculate spacecraft orientation.

Battery

In addition to solar arrays, M-Cubed receives power from four small Polymer Li-ION batteries onboard. These batteries each have a capacity of 3.89 Watt-hours (W-h) and were chosen over a larger battery due to their higher discharge rate and energy density. The cubesat requires a battery for the mission because the solar cells alone cannot produce enough power when peak power is needed. The battery also provides power to subsystems that cannot be turned off while M-Cubed is in eclipse. Although we anticipate M-Cubed to have a sun-synchronous orbit, there is a chance that M-Cubed is launched into an orbit with an eclipse period. The battery has been the primary driver of the thermal subsystem due to the small range of temperatures in which the battery can operate.